Research on the Relationship Between Modulation Depth and Center of High Order Harmonic in TDLAS Wavelength Modulation Method

Hao CHEN; Yu JU; Li HAN

doi:10.3964/j.issn.1000-0593(2021)12-3676-06

Journals >Spectroscopy and Spectral Analysis >Volume 41 >Issue 12 >Page 3676 > Article

Spectroscopy and Spectral Analysis
Vol. 41, Issue 12, 3676 (2021)

Research on the Relationship Between Modulation Depth and Center of High Order Harmonic in TDLAS Wavelength Modulation Method

Hao CHEN^{1、1; 2;}, Yu JU^3、3;, and Li HAN^1、1;

Author Affiliations

¹1. Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, China

³3. Beijing Aerospace Yilian Science and Technology Development Company, Beijing 100176, China

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DOI: 10.3964/j.issn.1000-0593(2021)12-3676-06 Cite this Article

Hao CHEN, Yu JU, Li HAN. Research on the Relationship Between Modulation Depth and Center of High Order Harmonic in TDLAS Wavelength Modulation Method[J]. Spectroscopy and Spectral Analysis, 2021, 41(12): 3676 Copy Citation Text

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Fig. 1. Second harmonic center amplitude, fourth harmonic center amplitude and modulation depth function curve

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Fig. 2. Simulation signals of the second and fourth harmonics under different air pressures

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Fig. 3. Schematic diagram of experimental device

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Fig. 4. Measured second and fourth harmonic signals at different air pressures

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Fig. 5. Curves of measured second harmonic and fourth harmonic center amplitude

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Fig. 6. Relative error curve of mean value of mp under different pressure conditions

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Pressure/atm	Theoretical/m	Measured/m	Relative Error/%	Theoretical/I₄_f/I₂_f	Measured/I₄_f/I₂_f	Relative Error/%
0.3	7.136 5	7.009 3	1.78	0.756 3	0.752 5	-0.50
0.5	4.281 9	4.218 0	1.49	0.629 4	0.625 1	-0.68
0.7	3.058 5	3.016 2	1.38	0.525 8	0.521 3	-0.86
0.9	2.378 8	2.347 0	1.34	0.441 4	0.436 8	-1.04
1.1	1.946 3	1.921 0	1.30	0.372 7	0.368 2	-1.21
1.3	1.646 9	1.625 8	1.28	0.316 6	0.312 4	-1.33
1.5	1.427 3	1.409 2	1.27	0.270 8	0.266 9	-1.44

Table 1. Theoretical and practical values of modulation depth m and harmonic center amplitude ratio under different air pressure

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Pressure /kPa	I₄_f (ν=ν₀)	I₂_f (ν=ν₀)	I₄_f/I₂_f	m
177.9	75.29	921.37	0.081 7	0.622 6
158.2	99.54	1 006.53	0.098 9	0.698 0
140.4	130.54	1 093.99	0.119 3	0.784 5
119.6	179.84	1 192.87	0.150 8	0.914 4
100.5	258.53	1 289.45	0.200 5	1.120 1
79.0	360.36	1 378.46	0.261 4	1.384 5
69.6	432.30	1 408.64	0.306 9	1.598 5
61.1	504.63	1 430.33	0.352 8	1.835 5
49.9	604.06	1 442.50	0.418 8	2.226 7
40.2	712.33	1 430.80	0.497 9	2.810 3
30.2	846.30	1 378.53	0.614 0	4.061 0
20.0	842.88	1 251.39	0.673 6	5.028 1
10.4	752.85	948.68	0.793 6	8.631 0

Table 2. Central amplitude, amplitude ratio and modulation depth m of the second and fourth harmonics under different air pressures

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